Enhanced visible-light photocatalytic activity of ZnS/S-graphene quantum dots reinforced with Ag2S nanoparticles

Today, contamination of water resources by pesticides and their presence in the food chain is one of the environmental problems. An economical method to eliminate of pesticides is the degradation in the presence of sunlight, which intensifies the need to design and manufacture new generation photocatalysts with short gap bands to accelerate the process of optical degradation. In this study, sulfur-doped graphene quantum dots (SG QDs) were successfully synthesized by the hydrothermal method and stabilized on the surface of ZnS semiconductor nanoparticles. Then, the core-shell structure of ZnS-SG QDs was decorated and reinforced with Ag2S nanoparticles. After confirming the structure of the prepared photocatalyst by X-ray diffraction (XRD), fourier transform infrared (FT-IR), scanning, and transmission electron microscopy (SEM & TEM) analyses, the photocatalyst's ability to optically degrade the two organophosphorus toxins diazinon and fenitrothion was evaluated. The results showed that the presence of Ag2S improved the photocatalytic activity and increased the degradation efficiencies to amount 40% for diazinon and fenitrothion. Furthermore, kinetic study showed that the photocatalytic degradation is initially followed by first order model and after that the mechanism is possibly changed to the second order model.